Methods of plasma formation are previously known in the art and may be selected from a group of comprising radio-frequency fields, microwave discharges, free-burning electric arcs, transferred electric arcs, high-intensity lasers, capacitively coupled electro-thermal igniters, DC glow discharges, and DC cold cathode discharges.
Methods for transferring energy to a precursor material by exposing a precursor material to the energy of a plasma are previously known in the art. Precursor material may be introduced into a plasma at any point. For example, a plasma may be created by a high intensity electric arc and a precursor may be introduced at any point of the arc column. In U.S. Pat. No. 3,209,193, the precursor material is introduced into the arc column of a free-burning plasma at the anode and U.S. Pat. No. 3,900,762 describes a working embodiment of the volumetric introduction of precursor into a plasma arc.
The precursor material may also be a consumable electrode. For example, in U.S. Pat. Nos. 5,460,701 and 5,514,349, a transferred electric arc between a cathode and a consumable anode is used to generate precursors in an elongated ionized arc that extends beyond the conduction columns.
Prior art teaches that materials formed by plasma techniques may have unusual properties. But prior art does not teach the synthesis of stoichiometric-nanostructured materials with controlled surface chemistry.
Materials produced by the method of this patent have surface chemistry characterized by a high aqueous dispersion stability, a low rate of hydrolysis, and a large zeta-potential. Materials produced by the method of this patent are stoichiometricly-nanostructured by the “active volume”. The “active volume” is in a plasma and is created by introducing an oxidizing gas into the plasma, before the plasma is expanded into a field-free zone, either (1) in a region in close proximity to a zone of charge carrier generation, or (2) in a region of current conduction between field generating elements, including the surface of the field generating elements. Energy is transferred from the plasma to a precursor material and at least one of a stoichiometric-nanostructured material and a vapor that may be condensed to form a stoichiometric-nanostructured material are formed in the “active volume”. The “active volume” is the most reactive part of the plasma and material synthesized in the “active volume” are stoichiometric-nanostructures with unique surface chemistry.
Stoichiometric-nanostructures or stoichiometriclly-nanostructured materials are defined as materials having controlled chemistry at the nanoscale. The chemistry of the nanostructured material may be controlled to be of full or partial stoichiometry, in the chemical sense, with respect to a reactant.
Prior art does not teach the introduction of oxidizing gas in a plasma to nanostructure materials to have unique surface chemistry. Instead prior art teaches away from the use of oxidizing gases in a plasma. For example U.S. Pat. No. 3,899,573 teaches the use of a reducing gas in the plasma created by a free-burning arc. The use of oxidizing plasma environments is conventionally discouraged because the materials used to generate the plasma are aggressively corroded. For example U.S. Pat. No. 4,642,207 discloses the use of an oxidizing plasma. But this process cannot be practiced in a manufacturing environment because aggressive corrosion rapidly renders process equipment inoperable. This is often the case even under conditions where shielding gas flows are used to protect specific process equipment as disclosed in prior art. The present invention teaches that judicious formation of an “active volume” enables the use of an oxidizing environment within the conduction column of a variety of plasmas to synthesize stoichiometric-nanostructured materials with unique surface chemistry.
Prior art does not teach the importance of forming at least one of stoichiometric-nanostructured material or vapor that may be condensed to form stoichiometric-nanostructured material in the “active volume” of a plasma. Instead prior art transfers energy from a plasma to precursors and forms nanoparticles by injecting at least one of a quench and a reaction gas:                after the plasma is expanded into a field-free zone; and/or        down stream from either (1) a zone of charge carrier generation, or (2) a region of current conduction between field generating elements.U.S. Pat. Nos. 5,460,701 and 5,514,349, use a transferred electric arc between a cathode and a consumable anode to generate an elongated ionized arc that extends beyond the conduction columns and injects at least one of a quench and a reaction gas into the elongated ionized arc. Other forms of the art introduce a reactive gas down stream from the “active volume” and form materials during thermal quench or gas phase nucleation. In all cases the art teaches the formation of materials in less reactive plasmas.        
Experiments in our laboratory indicate the “active volume” must be carefully controlled, to form before the plasma is expanded into a field-free zone, either (1) in a region in close proximity to a zone of charge carrier generation, or (2) in a region of current conduction between field generating elements, including the surface of the field generating elements, to derive the benefits of the reactive plasma and synthesize a stoichiometricly-nanostructured material with unique surface chemistry.